1. Field of the Invention
This invention concerns improvements in or relating to the friction welding of components.
In particular, the invention concerns a method for the manufacture or repair of a BLISK by linear friction welding.
2. Description of the Related Art
The two most commonly used methods for manufacturing BLISKs are machining from solid and attaching separately made blades onto a disk by friction welding. A further operation to remove upset or welding flash may be required as part of a finish machining procedure. Machining from solid is expensive and inevitably results in an unacceptable wastage of material, especially in the case of larger BLISKs. The method of present interest, in any case, can be employed as a repair technique to replace individual blades irrespective of whether a BLISK was manufactured from solid or fabricated using the same method. However, friction welding of blades onto a disk permits the blade and disk properties to be optimised, such as in a cast blade and a forged disk, and the use of dissimilar materials.
Methods for fabrication or repair of integrally bladed rotor assemblies involving providing a projecting stubs on the disk periphery are described in EP 376,874 (equivalent U.S. Pat. No. 4,873,751, and GB 2,218,016 (equivalent U.S. Pat. No. 4,883,216). Although the shape or configuration of the projecting stub is mentioned in both documents the top surface of the stub, which forms a joint surface, is not considered. The drawings contained in these patent specifications invariably show a planar top surface on the stub. However, EP 376,874 (and equivalents) does not mention linear friction welding as a possible joining technique, and GB 2,218,016 mentions it only as one of a possible list of techniques for heating the joint without any ensuing discussions whatsoever. In all instances, however, a weld force is shown acting xe2x80x9cdownwardsxe2x80x9d urging the new blade onto the stub in a generally radial direction. In order to avoid lateral displacement of one part relative to another in the joint or other distortion effects there is good reason to generate the weld joint surface in a flat plane perpendicular to a radial direction containing the applied weld force.
Gas turbine engine rotors are not normally designed with a cylindrical gas washed surface, thus a disk peripheral surface is almost always convergent, in one axial direction or the other, with the disk rotational axis. Furthermore, this surface may also be concave or convex and in some fan and low pressure compressor stages utilizing wide chord blades having a significant circumferential length the footprint of the blade on the disk surface is three dimensional and complex.
In friction welding the disk is clamped and, for example, a location on the disk periphery is presented to a welding station. At the welding station a blade clamped in a second item of tooling is rubbed against the disk surface to generate frictional heat at the interface. When a predetermined loss of length is achieved the blade is brought suddenly to a halt at a precisely defined location on the disk and is pressed against the disk for a short time to create the weld. When the assembly has cooled flash at the interface is removed and any required finish machining operations are carried out. If an airfoil has been damaged, e.g. by foreign object ingestion into an engine core, it is possible to remove a damaged blade and then to insert a replacement blade by the friction welding technique, thus avoiding the necessity of replacing a damaged BLISK in its entirety.
It is an object of the present invention to provide a way of using existing linear friction welding machines for original manufacture and repair, for example, of the aforesaid BLISKs having high hade angles and annulus curvature, while satisfying the required design and manufacture criteria. The xe2x80x9chadexe2x80x9d angle is the angle between the axis of a disk and tangent to a tapering disk peripheral surface.
According to one aspect of the present invention there is provided a method for the manufacture or repair of a BLISK in which a blade is attached by linear friction welding to a disk having a generally conical peripheral surface, comprising forming on the disk and the blade weld joint surfaces which during welding are urged into contact by a weld force, causing linear oscillation of the blade relative to the disk in a predetermined direction while simultaneously applying said weld force, characterised in that the disk weld joint surface is formed on the upper surface of an upstanding stub on the circumferential periphery of the disk at a substantially constant height above the disk periphery surface, the shape of the stub weld joint surface in axial and circumferential directions being determined according to the intersection of a blade envelope with the tapering periphery of the disk, and in a third direction by the locus of a straight line parallel to the predetermined direction of welding oscillation, and forming on the blade a weld joint surface complementary to the surface on the stub.
According to another aspect of the present invention there is provided a disk for a BLISK rotary stage of a gas turbine engine having formed on the circumference thereof at least one stub to which an airfoil blade may be welded in a friction welding operation wherein in axial and circumferential directions the edges of the platform conform to a shape defined by an intersection of a blade to be welded with the periphery of the disk and the upper surface of the stub is formed as a surface containing the locus of a line in a chosen direction of welding oscillation parallel to a surface tangential to the disk periphery.
According to a further aspect of the present invention there is provided a disk for a BLISK rotary stage of a gas turbine engine having formed on the circumference thereof a plurality of stubs spaced apart in a circumferential direction to each of which an airfoil blade may be welded in a friction welding operation wherein in axial and circumferential directions the stubs conform to an intersection of a blade to be welded with the periphery of the disk and the upper surfaces of the stubs are formed as a surface containing the locus of a line in a chosen direction of welding oscillation parallel to a chord of the blade.